The purpose of this study is to investigate whether some commonly used nonsteroidal anti-inflammatory agents (NSAIDs) affect blood levels of thyroid hormones. NSAIDs are medications used to treat painful conditions, such as muscle strains or arthritis. Some examples include aspirin, ibuprofen (Nuprin), and naproxen (Aleve). People who take NSAIDs may have changes in their blood levels of thyroid hormones, but it is not known how often this happens. The study will investigate 6 different NSAIDs, and participants may decide to receive one or more of the NSAIDs. If participants elect to receive one NSAID, the study will last 2 weeks. If participants elect to repeat the study with another NSAID, they will need to wait at least 6 weeks before repeating the study. Therefore, participation may last between 2 weeks and 1 year, depending on how many parts of the study are completed.